The embodiments described herein relate generally to an electric machine, and more specifically, to an electric machine having a sensor.
An electric machine is typically in the form of an electric generator or an electric motor. The machine typically has a centrally located shaft that rotates relative to the machine. Electrical energy applied to coils within the machine initiates this relative motion which transfers the power to the shaft and, alternatively, mechanical energy from the relative motion of the generator excites electrical energy into the coils. For expediency, the machine will be described hereinafter as a motor. It should be appreciated that a machine may operate as a generator and vice versa.
A stationary assembly, also referred to as a stator, includes a stator core and coils or windings positioned around portions of the stator core. It is these coils to which energy is applied to initiate this relative motion which transfers the power to the shaft. These coils are formed by winding wire, typically copper, aluminum or a combination thereof, about a central core to form the winding or coil. An electric current is directed through the coils which induces a magnetic field. It is the magnetic field that initiates this relative motion which transfers the power to the shaft.
For a variety of reasons including, for example, positioning, speed detection, and current sensing a sensor or transducer is used to determine the position of the rotor relative to the stator. One such sensor used in electric machines is a Hall effect sensor. A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications.
In its simplest form, the sensor operates as an analog transducer, directly returning a voltage. With a known magnetic field, its distance from the magnetic field generating component of the rotor, typically a permanent magnet, can be determined. Using groups of sensors, the relative position of the magnet can be deduced.
Hall sensors are commonly used in brushless DC electric motors to detect the position of the permanent magnet. For two equally spaced magnets, the voltage from the sensor will peak twice for each revolution. This arrangement is commonly used to regulate the speed of electric motors. Hall sensors are helpful to provide high starting torque in Electronically Commutated Permanent Magnet Motors, also known as ECPM motors.
Placing the Hall sensors close to the magnets is important to obtain a sufficient signal to the Hall sensors. Finding a rigid mounting for the Hall sensors close to the magnets is a challenge, particularly without compromising compact packaging of the motor.
The present invention is directed to alleviate at least some of these problems with the prior art.